The present invention relates to a plasma display (PDP) apparatus. More particularly, the present invention relates to a power supply circuit that generates voltages other than those supplied from the outside of the PDP apparatus.
The PDP apparatus has been put to practical use as a plane display, and it is expected that it will be used as a thin high-intensity display. FIG. 1 is a diagram that shows the general structure of a conventional three-electrode AC-driven PDP apparatus. As shown schematically, the PDP apparatus comprises a plasma display panel (PDP) 1 composed of two substrates, between which a discharge gas is enclosed, having plural X electrodes and Y electrodes adjacently arranged by turns with plural address electrodes arranged in the direction intersecting thereto and fluorescent substances arranged at the intersecting points, an address drive circuit 2 that applies such as an address pulse to the address electrode, an X common drive circuit 3 that applies such as a sustain discharge (sustain) pulse to the X electrode, a Vx voltage supply circuit 4 that supplies a voltage Vx, which will be described later, to the X common drive circuit 3, a scan circuit 5 that sequentially applies such as a scan pulse to the Y electrode, a Y drive circuit 6 that supplies such as a sustain discharge (sustain) pulse, which is to be applied to the Y electrode, to the scan circuit 5, a reset circuit 7 that supplies a reset voltage Vw, which will be described later, to the Y drive circuit 6, a control circuit 8 that controls each section, and a power supply circuit 9 that supplies various voltages such as Vs, Vw, Vx, and Va to each section. Since the PDP apparatus is widely known, a more detailed description of the whole apparatus is omitted here, but the power supply circuit that relates to the present invention is further described.
FIG. 2 illustrates the drive waveforms that show the signals to be applied to each electrode in the PDP apparatus. In the PDP apparatus, a display cell is formed at the intersecting point of a pair of an X electrode and a Y electrode and of an address electrode. The displaying operation is composed of a reset period in which each cell is put into a uniform state, an address period in which a cell to be displayed is selected, and a sustain (sustain discharge) period in which the selected cell is caused to discharge, and a continuous display is attained by the repetition of this series of operations.
As shown schematically, in the reset period, a pulse, the maximum voltage of which is Vw, is applied to the Y electrode while the X electrode and the address electrode are being kept to 0 V (ground level) and a discharge is caused to occur in every cell to attain a uniform state. In the address period, in the state in which the voltage Vx is being applied to the X electrode, a scan pulse, the voltage of which changes from the voltage Vs to the ground level, is sequentially applied to the Y electrode. By applying an address pulse of voltage Va to the address electrode of the cell that is made to emit light in synchronization with the scan pulse, a discharge is caused to occur in the cell that is made to emit light and wall charges are formed. In this way, a state in which all the cells correspond to the display data, that is, a state in which wall charges are formed in the cell that is made to emit light and wall charges are not formed in the cell that is not made to emit light, is attained. In the sustain period, in the state in which 0 V is being applied to the address electrode, a sustain pulse of voltage Vs is applied alternately to the X electrode and the Y electrode. (When the sustain pulse is not applied, 0 V is applied.) In the cell in which wall charges are formed, a discharge is caused to occur because the voltage due to the wall charges is added to the Vs, but no discharge is caused to occur in the cell in which wall charges are not formed.
FIG. 2 shows only an example, and various modifications of the drive waveforms are proposed. Moreover, the voltages Vs, Vw, Vx, and Va in FIG. 2 are specified adequately according to the structure and the intensity of the light emission of the plasma display panel and, for example, Vs is 150-180 v, Vw is greater than Vs, and Vx is also greater than Vs in the example shown in FIG. 2. In any case, it is necessary to apply plural high voltages to each electrode in the PDP apparatus, and the power supply circuit 9 supplies each high voltage. Although not shown schematically, the power supply voltage of the control circuit is 5 V (or 3 V) but this voltage is also supplied from the power supply circuit and a description is omitted below because it does not relate directly to the present invention.
The power supply circuit 9 generates the above-mentioned high voltages Vs, Vw, Vx, and Va by converting the AC input voltage from AC to DC, or first generates the voltage Vs, which needs a large current capacity, by the conversion from AC to DC, then generates Vw and Vx by converting the generated Vs from DC to DC. Generally, the latter method is employed. The voltage Va (Vx is also included when Vx less than Vs), which is less than Vs, can be generated from Vs with the aid of a step-down circuit. In this way, the operation is enabled only by the supply of the AC input voltage generally used as a voltage supplied from the outside. The small sized power supply device appropriate for the use in the PDP has been disclosed in Japanese Unexamined Patent Publication (Kokai) No. 6-332401. Moreover, in Japanese Unexamined Patent Publication (Kokai) No. 9-325735, a structure has been disclosed, which can reduce the power consumption due to the application of the sustain pulse between the X electrode and the Y electrode in the sustain period.
As described above, the power supply circuit in the PDP apparatus generates Vw and Vx by converting Vs from DC to DC, which has been generated by the conversion from AC to DC, therefore, a DC-to-DC conversion circuit composed of such as an oscillator circuit and a switching device is provided, this causing the circuits to be large in the PDP apparatus.
The object of the present invention is to reduce both the circuit size and the cost by simplifying the structure of the circuit to generate Vw and Vx.
In order to realize the above-mentioned object, the plasma display (PDP) apparatus according to a first aspect of the present invention comprises a secondary power supply that utilizes a pulse relating to the drive signal generated in an X drive circuit that drives a first electrode or in a Y drive circuit that drives a second electrode. By this characteristic, an oscillator circuit, a switching device, and so on, which are conventionally necessary to form the secondary power sources such as the power supply voltages Vw and Vx, can be eliminated, resulting in reductions in circuit size and in cost.
The pulse appropriate to be used by the secondary power supply is a pulse relating to the sustain pulse generated in the sustain period.
The secondary power supply is structured so as to comprise, for example, a charge-pump circuit that is driven by the above-mentioned pulse and a rectifier circuit that generates a direct current voltage by rectifying the output of the charge-pump circuit. In this case, if a charge-pump circuit equipped with plural stages that enter the output of the preceding stage as the base voltage of the subsequent stage is provided, it is possible to generate a voltage two or more times the voltage of the pulse to be used.
In another example of structure of the secondary power supply, a transformer, the primary of which is provided with a pulse, and a rectifier circuit that generates a direct current voltage by rectifying the output of the secondary of the transformer, are provided.
Moreover, if a voltage stabilizer circuit that converts the output of the rectifier circuit of the secondary power supply into a fixed voltage is further provided, an arbitrary voltage can be stably obtained.
The voltage generated by the secondary power supply generates either the voltage Vx to be applied to the first electrode in the address period or the voltage Vw to be applied to the second electrode in the reset period, or both.
As described above, conventionally the power supply voltages Vw and Vx are generally generated from the power supply voltage Vs to be used to generate the sustain pulse. However, the power supply voltage Va to be supplied to the address drive circuit is also generated, and it is possible to use Va as well as Vs to generate the power supply voltages Vw and Vx, and in this case, it is necessary to ensure the reliability of the circuit. The PDP apparatus in the second embodiment of the present invention will realize such a structure.
In other words, the plasma display (PDP) apparatus according to a second aspect of the present invention is characterized in that: a second power supply voltage (Va) is supplied to the address drive circuit; the second power supply voltage as well as a first power supply voltage (Vs) is supplied to both the X drive circuit and the Y drive circuit; and a circuit is provided, which passes a current from the path through which the second power supply voltage is supplied to the address drive circuit to the path through which the first power supply voltage is supplied to the X drive circuit and the Y drive circuit when the first power supply voltage is less than the second power supply voltage.
The circuit, which passes a current from the path through which the second power supply voltage is supplied to the address drive circuit to the path through which the first power supply voltage is supplied to the X drive circuit and the Y drive circuit, is a protection switch.
Normally, Vs greater than Va, but it may happen that Vs less than Va because Va rises prior to Vs due to the sequence of power on in the transition period such as power on and power off. In this case, it can happen that an abnormal current flows to the X drive circuit and the Y drive circuit via circuits that form the secondary power supply, but such an abnormal current can be prevented and a circuit malfunction, and so on, can be avoided according to the second aspect of the present invention.